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Cytocentric Visionaries: Roger Rönn

Part One: The Detrimental Effects of High Intracellular Reactive Oxygen Species on Hematopoietic Stem Cells.

This is a five-part series of blog posts containing excerpts from an interview that Dr. Alicia Henn, Chief Scientific Officer of BioSpherix, conducted with Roger Rönn, who is a promising student just finishing his PhD at Lund University. Our conversation was edited for brevity and clarity.

Roger attracted quite a bit of attention with his poster at ISSCR 2015 entitled “Improved Output and Functionality of IPS Derived Hematopoietic Progenitors by Multi-Layered Stress Inhibition.”

His findings and his enthusiasm were so compelling that we invited him to discuss his work here.

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Roger, why is your work so important?

RR: In our group, we are trying to make hematopoietic stem cells (HSCs) in the lab. Today with treatment against leukemia, the healthy HSCs are actually destroyed together with the cancer cells during the therapy. Re-introduction of functional HSCs is needed but transplants from another person carry the risk of graft vs.host disease. If we could tailor-make HSCs in the lab from a patient’s pluripotent stem cells, we can provide much improved therapeutics.

The HSCs we can make in the lab look very much like real HSCs, except for the most crucial thing, their ability to engraft and repopulate the host. They can only divide a few times, while a cord blood counterpart can give rise to maybe 300 times more progeny. There was an inferiority in the cells that we made in the lab compared to the real HSC. That bothered me a lot when I published my first paper.

You mean your Stem Cell Reports paper from earlier this year? [1]

RR: Yes. I think that there’s a risk that culture conditions that we are used to using, that are standardized in the lab and that we take for granted, actually lead to a functional degeneration of the cells that we make. Perhaps we would have succeeded [in making cells that were closer to real HSC] if we would have been more mindful of how we treat our cells.

If you compare HSC to their downstream progeny, they are extremely sensitive to stress. So I was curious. I selected different molecules to inhibit different specific stress pathways. Stress inhibition made an improvement in the fraction of HSC-like cells. So we’ve definitely confirmed that we have a stress issue.

Furthermore, it wasn’t just one of these molecules that did it. All of them did something good. That suggests that if we just target one particular stress pathway, the cell would still have plenty of alternative stress pathways that, when active, could negatively affect the cells.

And oxidative stress in particular?

RR: I read papers from 2007 [2] and 2011 [3] that indicated that reactive oxygen species (ROS) could be playing a role. They showed that functional HSC, directly from the body, have very low levels of ROS. As you culture these cells, the ROS level rapidly rises.

They could separate out cells that had the original low ROS from the cells with increased ROS and demonstrated that only the ones that had the ROS-low phenotype could actually engraft. All the other cells that were identical, except for the increased ROS level, were completely unable to give rise to any long-term engraftment.

So I would say this finding was crucial, that a high ROS level is incompatible with HSC engraftment.

That made me curious. If the ROS level rapidly rises, even if you just do short term culture of cells from within the body, what’s the ROS status of the cells that we generate over a long period of time completely in vitro?

I took fresh cord blood and compared it to cord blood that had been cultured for three days. I confirmed the same thing, a very rapid increase in ROS. I also saw that the vast majority of the blood cells that we create from iPS or ES cells were even higher than the highest ROS cells from cord blood.

Cultured HSC were higher in ROS than fresh cells?

RR: That was quite shocking because if almost 100% of the cells that we create are high in ROS, it is likely that we can’t expect these cells to ever work.

So my recent work is based on the philosophy that we need to fix the level of ROS that I believe mainly comes from the way we culture our cells.

 

In the next post, Roger talks with us about ways that he has found to decrease the exposure of cells to ROS.

 

1. Ronn, R.E., et al., Retinoic acid regulates hematopoietic development from human pluripotent stem cells. Stem Cell Reports, 2015. 4(2): p. 269-81.

2. Jang, Y.Y. and S.J. Sharkis, A low level of reactive oxygen species selects for primitive hematopoietic stem cells that may reside in the low-oxygenic niche. Blood, 2007. 110(8): p. 3056-63.

3. Yahata, T., et al., Accumulation of oxidative DNA damage restricts the self-renewal capacity of human hematopoietic stem cells. Blood, 2011. 118(11): p. 2941-50.

 

 Roger Rönn interview: Part 1, Part 2Part 3Part 4Part 5